KR101521508B1 - Fuel electrode which also serves as supporting body of solid oxide fuel cell, and fuel electrode-supported solid oxide fuel cell - Google Patents

Abstract

The present invention provides a fuel electrode that doubles as a support for a solid oxide fuel cell in which conductivity and strength are not easily lowered even if repeatedly exposed in a reducing atmosphere / oxidizing atmosphere. The fuel electrode serving also as a support of the solid oxide fuel cell of the present invention has a porous structure composed of first oxide particles having a 10% cumulative particle diameter of 5 占 퐉 or more and 12 占 퐉 or less and a 90% cumulative particle diameter of 84 占 퐉 or more and 101 占 퐉 or less, And electrode particles having an electrode catalytic function in which at least 10% and not more than 70% of the surface of the electrode particles are covered with the second oxide particles covering the surface of the pores.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a fuel electrode and a fuel electrode supporting solid oxide fuel cell that serve as a support for a solid oxide fuel cell,

The present invention relates to a fuel electrode and an anode-supported solid oxide fuel cell that also serve as a support for a solid oxide fuel cell, and a method of manufacturing the same.

A solid oxide fuel cell (hereinbelow, referred to as " SOFC ") that performs power generation by supplying an oxidizing gas including a heating gas such as hydrogen and oxygen to a fuel cell cell formed by separating a fuel electrode and an air electrode into a solid oxide electrolyte Quot;) is known. This SOFC is expected to be a next-generation fuel cell because it has a high power generation efficiency because it is operated at a high temperature and can generate fuel gas other than pure hydrogen.

In the SOFC, there are an electrolyte supported type cell in which an electrolyte is made thick and an anode supported type cell in which a fuel electrode is made thick. However, since an electrolyte has a large internal resistance at the time of power generation, Support type cells are becoming popular.

As the combustion poles of the anode-supported cells, nickel-zirconium (ZrO ₂ ) particles obtained by mixing nickel oxide (NiO with an average particle diameter of about 1 μm) and zirconia (ZrO ₂ ) particles having an average particle diameter of about 0.5 μm Cermet is known.

Patent Document 1 discloses a zirconia coarse particle group, a zirconia fine particle group, and a mixture of nickel and nickel oxide particle group, wherein the particle size of each of the above- Wherein the weight ratio of the zirconia coarse particles to the nickel particles to the nickel oxide particles and the zirconia particles is 7 to 4: 3 to 6: 1.

In addition, from the viewpoint of the charging of particles, there is a report on the effect of surplus voids on the packing density of the two-component mixture of fines and granules (Non-Patent Document 1).

Further, a technique for improving redox resistance by coating ceria around the core particles of nickel oxide has been proposed (Patent Document 2).

Further, a method of forming a fuel cell on a metallic porous body (Patent Document 3), a method of firing an electrolyte on a dissolvable diffraction material and then firing the electrode material to impregnate the electrode material (Patent Document 4) .

Japanese Patent Application Laid-Open No. 2009-224346 Japanese Patent Application Laid-Open No. 2010-251141 Japanese Patent Application Laid-Open No. 2005-174664 Japanese Patent Application Laid-Open No. 7-201341

 J. Ceram Jpn, 101 [11] 1234-1238 (1993)

During the operation of the SOFC, hydrogen is supplied to the fuel electrode, so that the fuel electrode is in a reducing atmosphere. However, at the start (start) stop, air reaches the fuel electrode. Therefore, in the use process of repeatedly operating and stopping the SOFC, the fuel electrode is repeatedly exposed repeatedly in the reducing atmosphere / oxidizing atmosphere, and Ni is oxidized as Ni, which is electrode particles of the anode, under the oxidizing atmosphere, It expands. The irreversible expansion of the electrode particles causes deterioration of the conductivity and strength of the anode, which is a cause of deterioration of battery characteristics and lifetime of the SOFC. Also, the slow agglomeration of the Ni particles in the repeated process of the reducing atmosphere / the oxidizing atmosphere deteriorated the battery characteristics of the SOFC.

Therefore, there is a demand for a fuel electrode which does not deteriorate in conductivity or strength even if it is repeatedly exposed in a reducing atmosphere / oxidizing atmosphere. However, according to the study of the present inventor, it has been found that the conventional nickel-zirconia cermet and the fuel electrode made of the fuel electrode material of Patent Document 1 do not sufficiently satisfy this requirement.

In view of the above-described problems, therefore, an object of the present invention is to provide a fuel electrode which doubles as a support for a solid oxide fuel cell in which conductivity and strength are hardly lowered even if repeatedly exposed in a reducing atmosphere / oxidizing atmosphere, and a production method thereof. It is another object of the present invention to provide a long-life anode-supported solid oxide fuel cell in which the cycle resistance of a fuel electrode is improved and a method of manufacturing the same.

The structure of the present invention to achieve the above object is as follows.

(1) A porous structure comprising a first oxide particle having a 10% cumulative particle diameter of not less than 5 μm and not more than 12 μm and a 90% cumulative particle size of not less than 84 μm and not more than 101 μm,

And an electrode catalyst layer having an electrode catalyst function in which at least 10% and not more than 70% of the surface of the electrode particles is covered with second oxide particles covering the inner surface of the porous structure of the porous structure. .

(2) The fuel electrode according to the above (1), wherein the electrode material is coated with 20% or more and 60% or less of the surface by the second solid oxide.

(3) A fuel electrode-supported solid oxide fuel cell comprising the fuel electrode described in (1) or (2) above, a solid oxide electrolyte membrane formed on the fuel electrode, and an air electrode formed on the solid oxide electrolyte membrane.

(4) A method for producing a honeycomb structured body, comprising the steps of: powdering a first oxide particle having a 10% cumulative particle diameter of not less than 5 占 퐉 and not more than 12 占 퐉 and a 90% cumulative particle diameter of not less than 84 占 퐉 and not more than 101 占 퐉; After obtaining a molded body from the slurry, the molded body is fired,

The porous structure comprising the first oxide particles and the second oxide particle covering the inner surface of the porous structure to obtain the fuel electrode having the electrode particles coated with 10% or more and 70% or less of the surface thereof Which is used as a support of a solid oxide fuel cell.

(5) A method for manufacturing a fuel electrode, comprising the steps of: forming a solid oxide electrolyte film on the fuel electrode; and forming an air electrode on the solid oxide electrolyte film, Type solid oxide fuel cell.

(6) The method for producing a solid oxide fuel cell according to (5) above, wherein the formation of the solid oxide electrolyte membrane is carried out by applying an electrolyte material on the formed body and firing the electrolyte material together with firing of the molded body .

According to the fuel electrode serving also as a support of the solid oxide fuel cell of the present invention, it is difficult to lower the conductivity and the strength even if it is repeatedly exposed in a reducing atmosphere / oxidizing atmosphere. Further, in the anode-supported solid oxide fuel cell of the present invention, the cycle resistance of the fuel electrode can be improved and a long life can be realized.

1 is a schematic view showing an example of the microstructure of a solid oxide fuel cell according to the present invention.
2 is an enlarged view of the circle R portion shown in Fig.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a fuel electrode and a fuel electrode-supported solid oxide fuel cell serving as a support of the solid oxide fuel cell of the present invention, and a method of manufacturing the same will be described.

(Fuel electrode and manufacturing method thereof)

First, a method of manufacturing a fuel electrode according to an embodiment of the present invention will be described. In this manufacturing method, a slurry is prepared from powders of yttria-stabilized zirconia (YSZ) particles serving as first oxide particles, powders of NiO particles serving as electrode particles having an electrode catalytic function, and zirconia particles serving as second oxide particles.

The dispersion medium of the slurry may be, for example, an organic solvent or a binder.

Here, it is assumed that the 10% cumulative particle size of the YSZ particles is 5 μm or more and 12 μm or less, and the 90% cumulative particle size is 84 μm or more and 101 μm or less. The average particle diameter of the NiO particles may be 0.5 to 5 mu m. The zirconia particles as the second oxide particles may be in the form of a sol or in the form of a powder. In the case of the sol, the average particle diameter of the dispersed zirconia particles is set to 0.1 μm or less. In the case of powder, the average particle size is set to 0.2 to 1.0 μm.

Further, in the present embodiment, the electrode particles are NiO in the manufacturing process step of the anode, but in principle, Ni is formed in the step of generating electricity by the SOFC. However, as described above, expansion due to an irreversible oxidation reaction in which Ni is converted into NiO in the process of using SOFC is a problem to be solved.

As the organic solvent, ethanol,? -Terpineol, butanol, or a mixture thereof can be used. As the binder, ethyl cellulose, polyvinyl butyral and the like can be used. Further, a plasticizer such as dioctyl phthalate or a surfactant may be added to improve moldability.

The slurry is molded by a predetermined method to obtain a molded body, and then the molded body is fired to obtain a fuel electrode.

A fuel electrode 10 according to an embodiment of the present invention which can be obtained by this manufacturing method will be described with reference to Figs. 1 and 2. Fig. The fuel electrode 10 includes a porous structure composed of zirconia particles 11 as first oxide particles and Ni particles 13 as electrode particles having an electrode catalytic function to cover the inner surfaces of the voids of the porous structure.

Nickel oxide having an average particle diameter of about 1 mu m and zirconia fine particles having an average particle diameter of about 0.5 mu m were slurried together with a foaming agent in a nickel-zirconia cermet, which is a conventional fuel electrode, and molded and fired to obtain a porous article. However, this fuel electrode does not have a strong skeletal structure and the bonding between zirconia fine particles / NiO is not strong. Therefore, the fuel electrode is repeatedly exposed repeatedly in the reducing atmosphere / oxidizing atmosphere, Ni is oxidized in the oxidizing atmosphere, and when the volume of the electrode particles swells irreversibly, the strength of the fuel electrode deteriorates as described above, And in the reducing atmosphere, agglomeration of the electrode particles progressed, resulting in deterioration of conductivity.

Here, in the fuel electrode 10 of the present embodiment, a skeleton having voids (pores) is formed inside the zirconia particles 11 as the first oxide particles. The zirconia 11 has the same thermal expansion coefficient as the material of the solid oxide electrolyte membrane 20 (described later) that has not been redox.

On the inner surface of the void, Ni particles 13 coated with zirconia fine particles 12 as second oxide particles as shown in Fig. 2 are coated with a predetermined ratio. Although the volume of the Ni particles 13 changes with the oxidation and reduction, the influence of the volume of the Ni powder 13 on the skeleton is small, as can be seen from the structure shown in Figs. 1 and 2.

That is, in the fuel electrode 10, the first oxide particles, which are not easily reduced even when the atmosphere is changed to a reducing atmosphere, are bonded to each other to form a skeleton, and electrode particles are bonded around the skeleton. Therefore, the influence of the volume change accompanying the redox reaction of the electrode particles on the skeleton is slight. Further, since the second solid oxide is present around the electrode particles, it also exhibits an action of suppressing aggregation of the electrode particles. It is considered that the fuel electrode 10 of the present embodiment can obtain the effect that the conductivity and the strength are hardly lowered even if the fuel electrode 10 is repeatedly exposed in the reducing atmosphere / oxidizing atmosphere based on such action.

As a first characteristic feature of the present embodiment, the zirconia particles 11 forming the skeleton have a 10% cumulative particle diameter of 5 占 퐉 or more and 12 占 퐉 or less and a 90% cumulative particle diameter of 84 占 퐉 or more and 101 占 퐉 or less. Since the first solid oxide becomes the skeleton of the electrode material, it is preferable that the 10% cumulative particle diameter is larger than the average particle diameter of the electrode material, and therefore, it is 5 m or more. If the 90% cumulative particle diameter exceeds 101 mu m, the proportion of the skeleton material increases, thereby obstructing the conductivity. When the 10% cumulative particle diameter exceeds 12 μm and the 90% cumulative particle diameter is less than 84 μm, the range of the particle size distribution decreases and the strength of the skeleton decreases. By having the above-mentioned particle size distribution, a strong skeleton formed by the first solid oxide having continuity is formed. The adjustment of the particle diameter distribution is based on a regular method.

In the second characteristic configuration of the present embodiment, the Ni particles 13 are covered with not less than 10% and not more than 70% of the surface by the zirconia fine particles 12. Hereinafter, this index is referred to as " coverage rate ". As a result, aggregation of electrode particles accompanying oxidation-reduction can be suppressed without lowering the activity of the electrode particles. That is, when the coverage rate is less than 10%, aggregation of the electrode particles can not be sufficiently suppressed, and when it exceeds 70%, the formation of the conductive path is hindered. The coating rate is preferably 20% or more and 60% or less.

Hereinafter, the coverage ratio is defined as the ratio of the second oxide concentration / (electrode material concentration + second oxide concentration) when the electrode particles are magnified with an electron microscope at an acceleration voltage of 25 kV 10,000 times magnification and quantitative analysis is performed by energy dispersion ), For example, Zr concentration / (Ni concentration + Zr concentration). The coating rate is adjusted by adjusting the amount of the electrode particles and the second oxide added in the raw material step.

The fuel electrode of the present invention preferably has a porosity of 20% or more and 60% or less. If it has a porosity within this range, gas diffusion property as a gas electrode is retained. If it is less than 20%, gas supply becomes insufficient, and when it exceeds 60%, mechanical strength is lowered.

The thickness of the fuel electrode 10 is not particularly limited as long as it can be used as the support of the SOFC, but it is preferably 0.2 to 5 mm. When the thickness is 0.2 mm or more, the fuel electrode can be reliably used as a support, and when the thickness is 5 mm or less, the fuel gas can be supplied to the surface of the electrolyte without excess.

Hereinafter, preferable conditions of the present embodiment will be further described.

The first oxide and the second oxide may be at least one selected from the group consisting of zirconia, alumina, silica, and ceria. However, it is preferable that zirconia is stabilized anyway. Examples of the stabilized zirconia include yttria stabilized zirconia (YSZ), calcia stabilized zirconia, and magnesia stabilized zirconia. The particle size is as already described. As the electrode particles, for example, nickel or nickel oxide powder can be used. It is also possible to use particles obtained by adding copper or cobalt to NiO particles. The particle size is as already described.

A method of obtaining a shaped body from a slurry is a wet method. A method of casting a slurry into a predetermined mold, a method of extrusion molding by adjusting viscosity, or a method of impregnating a sponge made of urethane or PVA having a mesh structure such as a skeleton structure, .

The firing of the molded body is carried out, for example, at a temperature of 1300 to 1500 占 폚 in the atmosphere for 1 to 10 hours. As a result, the ceramic component in the formed body and slurry is sintered to complete the final anode.

In the present specification, the " average particle size " refers to the particle size at the cumulative value of 50% in the particle size distribution obtained by the laser diffraction / scattering method (50% cumulative Particle diameter: D50), and regarding the sol, it is assumed that it conforms to the maker mark of a commercially available product to be used.

(Solid Oxide Fuel Cell and Method for Manufacturing the Same)

Next, a solid oxide fuel cell (SOFC) according to an embodiment of the present invention and a method of manufacturing the same will be described. This manufacturing method includes the steps of forming the solid oxide electrolyte membrane 20 on the fuel electrode 10 and the step of forming the solid oxide electrolyte membrane 20 on the solid electrolyte membrane 20 in addition to the steps in the method of manufacturing the fuel electrode 10 according to the present invention, A process of forming the air electrode 30 is performed. This manufacturing method is characterized by having the fuel electrode 10 shown in Fig. 1, the solid oxide electrolyte membrane 20 formed on the fuel electrode 10, and the air electrode 30 formed on the solid oxide electrolyte membrane 20 Supported SOFC (100) can be obtained. As described above, in the SOFC 100, the cycle resistance of the fuel electrode 10 is improved and a long life can be realized.

The production of the solid oxide electrolyte membrane and the air electrode can be carried out by a conventional method. Typically, a ceramic material such as YSZ is used as an electrolyte material, and the slurry is coated on the fuel electrode 10 and fired. In the case of the air electrode, (La _{0 .8} Sr _{0 .2} ) MnO ₃ may be used as a cathode material, and the slurry may be coated on the solid oxide electrolyte membrane 20 after firing and fired. Since the present embodiment is an anode supporting type, the thickness of the solid oxide electrolyte film 20 can be about 5 to 50 mu m.

Here, it is preferable that the molded body and the electrolyte material are made to be coextensive. That is, the fuel electrode 10 and the solid oxide electrolyte film 20 are simultaneously obtained by applying the electrolyte material onto the formed body before firing the molded body, and firing the molded body and the electrolyte material together. As a result, the shrinkage difference between the molded body and the electrolyte material can be reduced, and the occurrence of cracks can be suppressed.

Example

(Fabrication of fuel cell)

Preparation of fuel electrode slurry: A zirconia sol solution (zirconia concentration: 30 mass%, average particle diameter: 63 nm, ZR-30BS manufactured by Nissan Chemical Industries, Ltd.) was prepared. YSZ powder having a 50% cumulative particle diameter (D50) of 0.5 탆 and nickel oxide having a D50 of 5 탆 were mixed at a predetermined mass ratio. The mixed powder and the solution were mixed at a mass ratio of 8: 1 and stirred with a planetary mill to obtain a slurry. The mixing ratio of the YSZ powder and the nickel oxide was adjusted to obtain the coating rate shown in Table 1. The YSZ particles having the 10% cumulative particle size (D10) and the 90% cumulative particle size (D90) of Table 1 were added to this slurry in the same mass as the nickel oxide and were then stirred to prepare an anode slurry.

This anode slurry was dried, and then heat-treated at 500 ° C for 1 hour in the air. After crushing the obtained powder, the crushed powder, a pore forming material (10 μm PMMA particles, MX1000 manufactured by Soken Chemical Co., Ltd.) and 10% polyvinyl butyral α-terpineol were mixed at a mass ratio of 10: 1, and an anode sheet was produced by tape molding to obtain a formed body (thickness: 1 mm).

Preparation of electrolyte slurry: 5 g of polyvinyl butyral, 6 g of dioctyl phthalate, and 100 g of YSZ powder having a D50 of 0.5 m were mixed with 100 cc of isopropyl alcohol to prepare an electrolyte slurry.

An electrolytic slurry was applied to the molded body to form a film having a thickness of 50 m. Thereafter, the formed body was fired at 1400 DEG C for 5 hours in the atmosphere to complete the fuel electrode and the solid oxide electrolyte film at once.

Preparation of air electrode slurry isopropyl alcohol for 100cc polyvinylbutyral 10g, dioctyl phthalate _{6g, (La 0 .8 Sr 0} .2) MnO 3 And 50 g of yttria-stabilized zirconia were mixed to prepare an air electrode slurry.

An air electrode slurry was formed on the solid oxide electrolyte membrane to a thickness of 100 m. Thereafter, the resultant was fired in the air at 1100 DEG C for 3 hours to obtain a single cell.

≪ Evaluation of cycle resistance &

For each single cell thus obtained, the following oxidation-reduction cycle test was carried out. That is, in a power generation test apparatus maintained at 800 ° C, the fuel electrode side was maintained in a reducing atmosphere of 99.9% H ₂ for 30 minutes, then replaced with nitrogen, maintained in an oxidizing atmosphere of air for 30 minutes, did. Before and after the cycle test, measurement of conductivity and measurement of three-point bending strength were carried out for each single cell by the four-terminal method. Also, conductivity retention and strength retention were calculated before and after the cycle test. The results are shown in Table 1.

After the cycle test, evaluation was made under the condition that the conductivity was 300 S / cm or more, preferably 500 S / cm or more, and the three-point bending strength was 50 MPa or more, whereby the structure of the present invention was obtained.

In Table 1, 18, No. The comparative example 24 has a coating rate of 80% but satisfies the above evaluation criteria. However, none of the other data with the covering rate of 80% satisfied the evaluation criteria, so that the range satisfying the evaluation criteria was slightly reduced in the present invention, and the covering ratio was 80%.

The present invention is useful for the solid oxide fuel cell industry and various industries to which it can be applied.

10 Anodes also serving as supports
11 zirconia particles (first oxide particle)
12 zirconia fine particles (second oxide particles)
13 Ni particles (electrode particles)
20 solid oxide electrolyte membrane
30 air electrode
100 solid oxide fuel cell

Claims (6)

A porous structural body made of YSZ as a first oxide particle having a 10% cumulative particle diameter of 5 占 퐉 or more and 12 占 퐉 or less and a 90% cumulative particle diameter of 84 占 퐉 or more and 101 占 퐉 or less,
Characterized by having electrode particles made of NiO, which cover 10% to 70% of the surface by YSZ as the second oxide particle, which covers the inner surface of the porous structure, and also serves as a support of the solid oxide fuel cell Fuel electrode.
The method according to claim 1,
Wherein the electrode particles are coated with 20% or more and 60% or less of the surface by the second oxide particles.
A fuel electrode-supported solid oxide fuel cell comprising the fuel electrode according to any one of claims 1 to 3, a solid oxide electrolyte membrane formed on the fuel electrode, and an air electrode formed on the solid oxide electrolyte membrane.
A YSZ powder as a first oxide particle having a 10% cumulative particle diameter of 5 μm or more and 12 μm or less and a 90% cumulative particle diameter of 84 μm or more and 101 μm or less, a powder of electrode particles composed of NiO, and YSZ as a second oxide particle , The formed body is fired,
A porous structure made of YSZ as the first oxide particle and a fuel electrode having the electrode particles coated with 10% or more and 70% or less of the surface by YSZ as the second oxide particle covering the inner surface of the porous structure, Wherein the solid oxide fuel cell is a solid oxide fuel cell.
A method of manufacturing a fuel electrode, comprising the steps of: forming a solid oxide electrolyte film on the fuel electrode; and forming an air electrode on the solid oxide electrolyte film, A method of manufacturing a fuel cell.
6. The method of claim 5,
Wherein the formation of the solid oxide electrolyte membrane is performed by applying an electrolyte material on the molded body and firing the electrolyte material together with firing of the molded body.

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